Form 4 Biology Practice Paper: Cells, Enzymes, Transport And Nutrition

Form 4 Biology Practice Paper: Cells, Enzymes, Transport and Nutrition

2026-11-05

Form 4 Biology – 12 questions – 100 marks – 75 minutes

Form 4 Biology practice paper: 12 questions, 100 marks in 75 minutes on cell structure, enzymes, osmosis, diffusion, digestion and plant water transport, with full answers.

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Paper details　Form 4 Biology paper: 12 questions, 100 marks in 75 minutes on cells, enzymes, osmosis and digestion, with full answers and marking points.

Section A: Cell Structure and Enzymes

Answer all parts and show working with units in calculations.

#	Question	Answer and marking notes
1	The diagram shows a palisade mesophyll cell. (a) Name two structures present in plant cells but absent in animal cells. (b) Which structure controls the movement of substances into and out of the cell? (c) State the main function of the mitochondrion. (d) Explain why a mature red blood cell cannot carry out aerobic respiration for long.	(a) Cell wall and chloroplast, or large vacuole (2 marks). (b) Cell membrane (1 mark). (c) It carries out aerobic respiration, breaking down glucose to release energy (2 marks). (d) A mature red blood cell has no mitochondrion, so it relies on glycolysis in the cytoplasm and obtains only a small amount of energy (3 marks).
2	A student uses a x10 eyepiece and a x40 objective to view a guard cell, which measures 20 mm under the microscope. (a) Calculate the total magnification. (b) Calculate the actual length of the cell in micrometres. (c) If the x10 objective is used instead, what is the image length?	(a) 10 x 40 = 400 times (2 marks). (b) 20 mm / 400 = 0.05 mm = 50 micrometres (4 marks). (c) 20 mm x 100/400 = 5 mm (2 marks).
3	Enzymes are biological catalysts. (a) State two properties of enzymes. (b) Amylase activity rises from 20 to 40 degrees Celsius but falls to zero at 80 degrees. Explain both changes. (c) Explain why one enzyme usually catalyses only one reaction.	(a) They are proteins, specific in action, reusable, and affected by temperature and pH (any two, 2 marks). (b) At 40 degrees the molecules have more kinetic energy, so enzyme and substrate collide more often and the rate rises (2 marks); at 80 degrees the enzyme is denatured, the active site changes shape and the substrate cannot bind, so the rate falls to zero (3 marks). (c) The active site is complementary only to a specific substrate, forming an enzyme-substrate complex (2 marks).
4	A student investigates the effect of pH on amylase: amylase solution is mixed with buffer solutions of different pH, starch solution is added, and samples are tested with iodine solution every minute. (a) State the independent and dependent variables. (b) State two controlled variables. (c) Explain why iodine solution is used instead of Benedict solution. (d) Predict the difference between the results at pH 2 and pH 7.	(a) Independent variable: pH; dependent variable: the rate at which starch is broken down, that is the time for the iodine colour to fade (2 marks). (b) Temperature, enzyme concentration, starch concentration and reaction time (any two, 2 marks). (c) Iodine solution detects starch directly, while Benedict solution tests for reducing sugar and does not show how much starch has been digested (3 marks). (d) At pH 2 the enzyme is denatured, starch is not digested and the iodine stays blue-black; at pH 7, close to the optimum, starch is digested quickly and the iodine fades sooner (2 marks).

Section B: Movement of Substances

Answer all parts; in explanation questions state the mechanism.

#	Question	Answer and marking notes
5	Four potato strips, each 4.0 cm long, are placed in distilled water and in 0.5 mol per dm3 sucrose solution, and measured after 30 minutes. (a) Predict and explain the change in each group. (b) The strip in sucrose measures 3.6 cm; calculate the percentage change in length. (c) What would happen if a boiled strip were placed in distilled water?	(a) The strip in distilled water lengthens because the water potential outside is higher than inside the cells; the strip in sucrose shortens because the external water potential is lower (3 marks). (b) (3.6 – 4.0) / 4.0 x 100% = -10% (3 marks). (c) Boiling damages the cell membranes, so osmosis cannot occur and the length stays unchanged while the tissue softens (2 marks).
6	Compare diffusion and active transport. (a) Give three differences. (b) Which process moves mineral ions into root hair cells? Explain. (c) Explain why active transport requires oxygen.	(a) Diffusion moves down a concentration gradient, needs no energy and its rate depends on the gradient; active transport can move substances against the gradient, uses ATP and needs carrier proteins (3 marks). (b) Active transport, because the mineral concentration in the soil is lower than in the root cells yet ions are still absorbed (3 marks). (c) The ATP needed is supplied by aerobic respiration, so a lack of oxygen limits the ATP supply (3 marks).
7	Name three digestive enzymes, state where each is secreted and which substrate it acts on, and describe the role of bile in fat digestion.	Amylase is secreted by the salivary glands and the pancreas and breaks starch into maltose (2 marks); protease is secreted by the stomach glands and the pancreas and breaks protein into polypeptides (2 marks); lipase is secreted by the pancreas and breaks fat into fatty acids and glycerol (2 marks). Bile is made by the liver and stored in the gall bladder; it emulsifies fat into small droplets, increasing the surface area for lipase. Bile contains no enzyme (2 marks).
8	Features of the villi of the small intestine. (a) State three structural features and their advantages. (b) Which blood vessel carries glucose and amino acids away, and to which organ? (c) Why do the epithelial cells contain many mitochondria?	(a) Villi increase the surface area, microvilli increase it further, and the thin epithelium with a rich blood supply shortens the diffusion distance (3 marks). (b) The hepatic portal vein carries them to the liver (3 marks). (c) Absorption is largely by active transport, which needs a large supply of ATP (3 marks).

Section C: Nutrition, Absorption and Plant Water

Answer all parts; answer comparison questions point by point.

#	Question	Answer and marking notes
9	Food tests. (a) Name the reagent used to test for reducing sugar, starch, protein and fat. (b) Describe the positive result of the protein test. (c) Why is the filter paper dried when testing for fat?	(a) Reducing sugar: Benedict solution; starch: iodine solution; protein: biuret reagent; fat: filter paper test or Sudan III (4 marks). (b) The colour changes from blue to purple (2 marks). (c) Drying evaporates the water so the translucent oil stain left behind can be seen clearly (2 marks).
10	A plant absorbs 0.80 g of carbon dioxide by photosynthesis during the day and releases 0.30 g by respiration at night. (a) Calculate the net carbon dioxide uptake over the whole day. (b) Explain why no net uptake is measured at night. (c) Give three differences between photosynthesis and respiration.	(a) 0.80 – 0.30 = 0.50 g (2 marks). (b) There is no light at night, the light-dependent stage stops, photosynthesis cannot occur and only respiration releases carbon dioxide (2 marks). (c) Photosynthesis occurs only in light, takes in carbon dioxide, releases oxygen and stores energy; respiration occurs day and night, takes in oxygen, releases carbon dioxide and releases energy (4 marks).
11	Water movement from root to leaf. (a) State the cause of the transpiration pull. (b) Explain why leaves wilt after a ring of bark is removed. (c) State one advantage of stomata closing at night.	(a) Transpiration from the stomata lowers the water potential of the mesophyll cells, setting up a gradient from root to leaf that pulls the water column upwards (3 marks). (b) Ringing removes the phloem so organic nutrients cannot reach the roots, the root system is damaged and water uptake falls (3 marks). (c) It reduces water loss, although carbon dioxide uptake also falls (2 marks).
12	A person sweats heavily after vigorous exercise. (a) Explain why a drink containing electrolytes is better than distilled water. (b) State two ways the kidney maintains water balance. (c) What would happen to the blood if only a large volume of distilled water were drunk?	(a) Sweat contains sodium and chloride ions; replacing water alone dilutes the blood and the electrolyte concentration becomes too low, affecting nerve and muscle function (3 marks). (b) More antidiuretic hormone makes the collecting duct reabsorb more water, and the kidney produces less urine (3 marks). (c) The water potential of the blood rises, water enters the cells and they may swell (2 marks).

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